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Intensity (a.u.) 1,0 0,8 0,6 0,4 0,2 D. Kaskelyte et al. / Medical Physics in the Baltic States 7 (2009) 20 - 23 1,2 PKH67 cells suspension gelatin differential spectrum 0,0 480 500 520 540 560 Wavelength (nm) Fig. 6. Fluorescence spectra of stained myogenic cells, a slice of gelatine and obtained differential spectrum (upper plot). Spectra are normalized to 540 nm. Set of fluorescence intensity of PKH67 stained cells in layered specimen collected at different probing depths of a fiber tip (bottom view, bottom plot). A plot (bottom view, the upper section plot) represents the distribution of the fluorescence intensity of the marker registered at 506 nm along the layered specimen. 23 The difference in fluorescence intensity value at 506 nm represents the ability to localize and to evaluate the spatial localization of the PKH 67 stained fluorescing myogenic cells in light scattering environment. 4. Conclusions The constructed portable unit for fluorescence measurements could provide the real-time monitoring of fluorescing objects in biological tissue at various probing depths. The facility for accurate targeting of the position of the stained cells, which has been demonstrated within scattering layered environment, may improve the performance of fiber-probe based equipment as a diagnostic tool, utilizing the fluorescence spectroscopy method for the detection of labelled cells in biological tissue in real time regiment. 5. Acknowledgement This study has been supported by the Lithuanian State Science and Studies Foundation, the grant No. B- 07041. 6. References 1. Utzinger U., Richards-Kortum R., “Fiber optic probes for biomedical optical spectroscopy”, J. Bio. Opt. 8, 2003. p. 121-147. 2. Pfefer T.J., Schomacker K.T. etc., „Light Propagation in tissue during fluorescence spectroscopy with single-fiber probes”, IEEE J. Select. Top. Quant. Electr. 7(6), 2001. p. 1004- 1012. 3. Kaškelytė D., Čiburys A., Bagdonas S., Streckytė G., Rotomskis R., Gadonas R., Fiber-optics based laser system for 2-D fluorescence detection and optical biopsy, Med Physics in Baltic States: Proceedings of the 6th International conference on medical physics, 10-11 October, Kaunas 2008, p. 12-14.
MEDICAL PHYSICS IN <strong>THE</strong> BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania CdTe QUANTUM DOTS STABILIZATION BY PROTEIN IN AQUEOUS SOLUTION Vilius PODERYS * , **, Deividas MOTEKAITIS**, Ričardas ROTOMSKIS* , ** * Institute of Oncology Vilnius University, Laboratory of Biomedical Physics; **Vilnius University, Physics Faculty, Quantum Electronics Department, Biophotonics laboratory Abstract: Quantum dots – semiconductor fluorescent nanoparticles are very promising fluorescent markers due to their unique properties. It is very important to know bioeffects of quantum dots before using them in medicine, however it is still very little known about interaction of quantum dots with biomolecules. In this work we investigated stability and spectral properties of CdTe quantum dots in aqueous media and effect of quantum dot – protein interaction on these properties. We showed that BSA stabilizes CdTe quantum dots. Keywords: Quantum dots, bovine serum albumin, fluorescence spectroscopy, quantum dot – protein interaction 1. Introduction Since the first time fluorescent semiconductor nanoparticles (quantum dots) were synthesized, they are widely explored due to their possible applications in many fields, including medicine. Tunable emission wavelength, broad absorption and sharp emission spectra, high quantum yield (QY), resistance to chemical degradation and photobleaching, versatility in surface modification makes quantum dots very promising fluorescent markers [1]. Quantum dots can be used for live cell labelling ex vivo, detection and imaging of cancer cells ex vivo [2], as a specific marker for healthy and diseased tissues labelling [3], for labelling healthy and cancerous cells in vivo [4], and for treatment of cancer using photodynamic therapy [5]. Despite all unique photophysical properties, some problems must be solved before quantum dots can be successfully applied in medicine. Quantum dots usually are water insoluble and made of materials that are toxic for biological objects (Cd, Se). To make them suitable for application in medicine surface of quantum dots has to be modified to make them water-soluble and resistant to biological media. After injection of quantum dots to live organisms they are exposed to various biomolecules (ions, proteins, blood cells, etc.). This could lead to degradation of quantum dot coating or quantum dot itself. In this case toxic Cd 2+ ions are released and can cause damage to cells or even cell death. It is very important to know the bioeffects of quantum dots before using them in medicine. Till now 24 it is still very little known about the interaction of quantum dots with biomolecules. Recently the interaction of quantum dots with biomolecules attracted much interest and is studied using various methods, such as atomic force microscopy, gel electrophoresis, dynamic light scattering, size-exclusion high-performance liquid chromatography, circular dichroism spectroscopy and fluorescence correlation spectroscopy [6-9]. In this work we investigated stability and spectral properties of water-soluble CdTe quantum dots coated with thioglycolic acid in aqueous solutions (deionized water and saline) and in model media (deionized water and saline with bovine serum albumin). 2. Materials and methods Quantum dots solutions were prepared by dissolving CdTe-TGA quantum dots (λ =(550 ±5) nm, PlasmaChem GmbH, Germany) in deionized water or saline (0.9%), and diluting further till required concentration. Prepared solution was divided in two parts. A small amount of concentrated bovine serum albumin (BSA) (BSA, V fraction, M = 69000 g/mol, Sigma, Germany) solution (in deionized water or saline) was added to one solution and equal amount of solvent was added to another. Deionized water was prepared using two stage water cleaning system (distiller GFL 2008, Germany and deionizer MicroPure, TKA, Germany). pH values of solvents were 6 and 5.6 for deionized water and saline respectively. Spectral measurements were performed immediately after preparation of solutions. Absorbance spectra were measured with Varian Cary Win UV (Varian Inc., Australia) absorption spectrometer. Photoluminescence
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